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Allan G, Cyborg, gavin eisler, JER.Hill, kevin, kommando, Mark Parker, NYBSAGUY
Total Likes: 25
Original Post (Thread Starter)
by gavin eisler
gavin eisler
Hi there,
My 1971 Devimead lightning is due some TLC, the bike currently has not run for a few years and needs excavated from the back of a friends shed. It was running when it was put away but will need a new battery and carb cleaning at the very least.
This thread will be about small time resurrection , with a bonus feature of replacing the old worn Devimead 750 barrels with brand spanking new Alloy barrels supplied by John Hill.
The following pics are shots of the barrels in my secret underground layer.
The barrels were cleaned with a citrus based cleaner then blow dried.[Linked Image]
[Linked Image]
[Linked Image]
Here they are posing in the turbine pit of Unit three, thats the reg ring and machine shaft in the cage[Linked Image]
All clean now
[Linked Image]
Riding on a barra in the machine hall[Linked Image]
Liked Replies
by gavin eisler
gavin eisler
Heres a wee update.
The bike continues to run V well, it has a wee weep from the front of the rocker cover, will fit a new gasket the next time I look at the tappets.
Its totally reliable, easy to start and doesnt hing about.

Things that arent working.
The speedo, despite a new cable and drive gearbox the speedo now under reads and struggles to get beyond 50 mph, I suspect the female square drive bush in the head is rounded out.
Thats it. To be fair to the repop speedo this probably started because the previous speedo cable had an under sized square drive end, pattern shite.
The engine breather.beyond 5 K its an oil leak.

The bike is 50 this year, made in June 71, to celebrate I allowed the police to caution me for speeding on the road from Dunoon to Inverary,
they were very nice about it,( I was very polite) let me off with a long look at the bike. The nice older one noticed the non stock front brake lever, the other one looked like he would have jailed me if he wasnt being trained.Un marked black Bee Em, stealth rozzers.

Twin discs, YAYYY, I might not be writing this now if I still had the front drum, twice lately I have rounded a corner to be confronted with a large vehicle straddling the road ( not a minor back road, the main efFing road), first time was a camper Van ( I really detest these traveling road blockers), second time was a road menders lorry making a 3 point turn because he was too lazy to drive a mile to a realistic turning point. both times the front rubber held, but made noises you dont want to hear.

lately our roads have become more loaded than normal, staycation means every day is National Bad Drivers day, sadly the weather has been great this Summer , this means they will probably return in years to come,

feed back on mods.
Kommandos forks guts, brill.
Twin discs, life savers.
new kick start, V comfy
new gear pedal, still hasnt fallen off and still doesnt waggle, the replacement spline stub I have remains in its bag.
Barrels, brill ( watch your licence!)
Big valves and porting, its definetely quicker than before , still got 30 mm carbs, its not getting bigger carbs until i fit the MAP con rods, untill then I am loving the flexible grunty motor, it never needs to go past 6 K.
End feed , Brill
Non Lucas electrics, Brill.
5 speeds, brill
7 plate clutch,brill.
Electric tach, brill
Now wash your hands.
3 members like this
by BrizzoBrit
I've found flipping the side the cotter is inserted from gives several degrees of difference in kickstart angle for fine tuning purposes.

I've also found the trick to making cotter pins last as they all seem be made of cheese is to tap them in, tighten the nut moderately, wiggle the lever, tap the cotter (fat end :)) using a long punch which saves the end of the cotter and your timing cover and repeatt this. Use the punch and hammer to seat it rather than trying to pull it into place with the nut. Stripped thread abound with that method.

This is probably the correct procedure, but it was forced on me in a Darwinian way.

2 members like this
by DJinCA
Gavin, glad you are still with us, at least for now. I do enjoy this thread and your shared knowledge is an asset to all. Thanks for reconsidering.

kevin, no you are not the only one that does that, and drunken internet purchases are about equally frightening.

1 member likes this
by Magnetoman
A good thing about this site is it usually gets quick responses to questions. That said, it requires having read a number of responses from a given person to a variety of questions to know how much to weigh their answers, no matter how confidently they might be presented.

At one extreme, it would be foolish not to take very seriously anything John Healy writes about carburetors, and at the other extreme there are a few people whose posts I no longer even glance at because the odds are high that whatever they write is incorrect. Another group only uses the site as their social media outlet. Although those people sometimes include technical information, it's typically just a repetition of what they read elsewhere so I don't glance at them, either.

I've met a few people on Britbike and know of their skills from that or other evidence (e.g. Chaterlea25 rebuilt my C15S in Ireland and was team mechanic on the Cannonball), but most people are just avatars on the web. However, picking a few names from recent Projects forum threads, people such as you, R Moulding, George Kaplan and Cyborg (and others) provide details of their own projects so they've "earned" credibility for their technical answers since they've established in that way that they actually know how to work on motorcycles themselves (and not just in a bolt-on-parts sort of way).

These things aren't unique to Britbike. I follow a few other motorcycle sites (e.g. Ariel and a lesser marque) and the same types of posters are to be found there as well, although in different ratios on each site. However, of the over 11,000 members listed as being on this site, it seems to me that fewer than 1% are responsible for at least 90% of the technical content.

I haven't noticed him for a while, but there used to be a guy who would swoop in occasionally with questions about work he was doing on customers' bikes. He never contributed anything to Britbike, only took information from it (which may or may not have been correct), so I didn't feel compelled to respond to his questions. After all, he was being paid so why work for free for him? Your point is along the same lines, i.e. why should you actually have to pay in order to provide all the technical content that you do that ~11,000 people read for free? I don't have an answer for that question.
1 member likes this
by gavin eisler
gavin eisler
Its now wintery , the Woodcock are back in the woods and its pissing down.

I have accumulated a new set of front pipes , supplied by Grin, offered up to the spare head they look as if they might fit, balance stubs are not cock eyed, the label on the wrapper says LF Harris, fingers crossed they might work.

The bike has been pretty much faultless over the year, I had one blown dip filament, easy fix, noted that the Quadoptic reflector had parted company with the bulb holder, probably due to the tight squeeze in the flat back lamp, massaged and glued back into place.
on a decent 100 mile loop with an SV 650 for company the SV rider was complimentary about the beesa zest.
Due to the plague its not done may miles this year , only one oil change and no worn out rubber.
After the halcyon clear skies and empty roads of the Spring lockdown , the Summer season has seen even greater numbers of oversize campers driven by folk with limited ability, our local pier has turned into a " free camping " litter and excrement waste land. Locals are raging.

Winter project, refurb a spare head, to be fitted with Mic carb adaptors to take the OKO flat slides, carb studs switched for 5/16 BSF x 1/2 long cap screws to suit same.
5/16 rocker bolt threads , one was stripped, all now drilled out and helicoiled for 5/16 UNF as per the existing head.
The spare seems to be pretty low mileage, pipes fit tight in the zorst ports.
Thanks to Mark Parker i have some sketch guidance for the inlet mods, and at his suggestion I have bought Dave Vizards porting book. Plan is to make a crude flow bench and test stock versus modded, this should while away the dreich days.
I am reluctant to go for the biggger inlet valves ( 44 mm ) , it was a ball ache the last time, involving sinking the valves into the head to get the correct spring fit , MPs experiments suggest that far more flow is available just by getting the port shape right, and since the seats are in A1 condition I am staying with the stock 40.5 s for now.

As part of the flow tests I have also accumulated a set of spare air boxes , luckily these are V cheap, I am intrigued to find out what effects they may or may not have.

before i fit the shiny new pipes I hope to fit an AF ratio set up using the old pipes, any hints on what, who and where to get them would be appreciated.

The brexit archery prep is going well, set a new SFAA record in Veteran Bare Bow, goin round the woods regularly is helping keep the weight off , stops my knee dislocating ( nae LHS posterior cruciate) and stops me going mad from cabin fever.
1 member likes this
by pushrod tom
pushrod tom
A few years ago I settled on an AEM . Simple, compact and reliable. I mounted it as softly as possible in an original BSA instrument cup. I know I will get some crap about this but the sensor was mounted in the middle of the balance tube. This worked well also and the info was checked against data from the dyno..I also like the pencil/paper data recording but you must be very careful to watch where you are going at the same time as glancing at the meter. I had a few close calls! I think it is quite possible to get these bikes to run well with old school practices but for an enthusiast project, collecting and applying data can be lots of fun. I know you will keep us posted. PRT
1 member likes this
by Magnetoman
Originally Posted by Cyborg
Wonder if there is a reasonably inexpensive analog voltmeter out there. Reading lambda voltage.... I recall this being discussed at one point ...
I don't remember that discussion, but it must(?) have been mentioned at the time that the sensor still needs to be supplied with regulated 12V for its heater, and that the lambda voltage isn't linear so it would require writing notes at 60 mph to later use with a look-up table to extract AFR. I'm afraid by the time someone had pursued this approach to a useful end they would end up reinventing a commercial AFR unit.

Originally Posted by gavin eisler
I knew it was written up somewhere,
I skimmed through the folder containing images for that thread and didn't see one of my throttle mechanism, so here it is:

[Linked Image]

The long brass rod and clamp allows me to attach the unit to the handlebars any of my bikes despite their variations in shape and positions where the levers and mirrors are mounted. The bottom of the Al plate is machined concave to further keep it in position and, together with the clamp, I've never had a problem with it moving

A 50 kΩ potentiometer has a 1.5 V AA battery across it so it draws 30 µA when in use, meaning each battery is only good for ~100 hours of continuous use. Since on a given day it's only in use for a few hours, rather than bothering with an on/off switch I leave it connected the entire time, and then at the end of a day I pull the battery out of the holder. For long term disuse I leave the battery in the holder (to keep it from disappearing at the bottom of the box) but use a piece of blue tape between the battery and holder to disconnect it.

The DC signal from the potentiometer comes from the "wiper," so could vary by a maximum of the full 1.5 V, although the actual range is determined by the ratio of diameters of the brass "pulley" on the potentiometer (0.75") to the throttle grip. The potentiometer I used has a full range of a little more than ¾-turn. Fatter grips will turn it more and thinner grips less so the 0.75" I used for the brass pulley isn't arbitrary. It lets the unit work on my various bikes without running out of movement on the potentiometer. Since the only force the string is subjected to is what's necessary to turn the potentiometer, slipping isn't a problem. However, I wrap the string twice, and since the rotation of the grip is small enough that some of the string doesn't get pulled away, I add a bit of tape for a belt-and-braces installation.

Assume on a given bike the full range between 0 and full throttle ends up, say, 1.3 V. That means between 1/16" throttle and 3/16" throttle (i.e. either side of the 1/8 throttle point) the voltage ranges between 80 mV and 244 mV. That range lets me determine the actual throttle position in this region to more than sufficient accuracy for using the AFR readings to determine the jetting. Although the further the slide moves past the 1/8 position the less critical its precise location is for determining jetting, the same level of precision is there over the entire range of throttle opening.
Attached Images
1 member likes this
by gunner
The PWK is a good carb, perhaps not as sophisticated as a Mikuni VM, but easy to tune and plenty of genuine Keihin parts available cheaply.

I'm running Amal 930's on my A65, a Mikuni VM 34 on my Commando and a JRC PWK 28 on my B44.

In terms of quality the PWK is similar to the Mikuni but there are a multitude of cheap far eastern replicas to confuse things. The JRC version seems good as does the OKO type. Luckily the genuine Keihin jets seem to fit all replicas and there is a nice chrome flat slide you can get. The PWK also comes with a separate choke circuit to make starting easy.

So for me the PWK is as easy to tune as Amal Concentric but better quality and alot cheaper than a Mikuni.

With all the AF ratio kit youre going to get I'm sure you will have them running flawlessly.
1 member likes this
by kevin
i have a mild street cam in that motor, 282 degrees overlap, and the lean readings were out of the middle of a 2 into 1 muffler. i dont think theres a strong negative pulse. richer readings up in the header pipe about ten inches from the head. you could just take an old pipe and check inner temperature with an inexpensive thermocouple stuck in from the end. amazon sells them.

but the only difference was in the magnitude of the actual number. for setting carbs where you wanted to achieve a correct mixture it works. fine just find a benchmark main jet for example that worked right, then read the gauge and look for that same number ot slightly leaner down through the throttle settings

i could probablytweak the sensor position to achieve textbook values, but its not fuel injection after all.

the AF meter makes setting carbs super easy, especially needle jet, needle and slide.

i just remembered i have an old colortune mica sparkplug that i could calibrate the AF meter with. if i had a brain i would have done that last time
1 member likes this
by gavin eisler
gavin eisler
Trying out Postimage as a host.
Pics of Head , airbox, carb, rubbers. Seems to work OK, sorry about the poor lighting. Carbs are 32 MM OKO flatslides, mounted with mik flange adaptors, , air box linked with silicone hose over carb inlet and sleeved to T140 rubbers

url=][Linked Image from][/url]

[Linked Image from]

[Linked Image from]

[Linked Image from]
1 member likes this
by Magnetoman
Originally Posted by Cyborg
“One” could measure the A/F ratio with the probe and then (probe removed) measure it with the wideband sensor. That wouldn’t necessarily tell you much about how far air is getting back up there, but it would give you an idea of how much observer effect is caused by the probe.
At the risk of continuing to hijack Gavin's thread, it's important to understand that in the discussion so far we've been mixing two separate issues.

Because of how a wideband sensor works it is extremely sensitive to any amount of fresh air that reaches it. It's not that some amount of reversion that reaches the sensor will cause some amount of error, any amount of reversion will cause a huge error that is impossible not to notice. The issue Gavin faces is where to install the probe. It has to be far enough upstream that pulses of fresh air can't reach it, but far enough downstream from the head that it doesn't receive excessive heat from the exhaust that would affect the readings even if it didn't damage the sensor. Luckily, it appears to me there is quite a lengthy sweet spot with any of our engines for installing the sensor.

In this thread Cyborg and I mostly have been musing about how much the "observer error" of a separate probe in the exhaust stream will affect how far the fresh air will get sucked back up the pipe. Irrespective of the answer to that, if the sensor is further upstream than that, what it will accurately measure is the AFR of the exhaust gas. However, a separate, but quite relevant, question Cyborg and I have discussed elsewhere is how much the downstream restriction caused by a separate probe might actually affect the AFR. Similar, but to a lesser degree, to the effect of a restrictive silencer, the probe will affect the pressure pulses that make it to the exhaust valve to inhibit fresh mixture from exiting during the valve overlap. This is relevant because the amount of fresh fuel that escapes into the exhaust pipe during that overlap will affect the AFR in the exhaust stream.

For those who don't want to sacrifice a pipe to install a bung (or two pipes, for Gavin's A65), the issue is how much the AFR readings might be affected by the effect on the pressure pulses of using a separate probe inserted past the point of reversion. Unfortunately, I doubt if measurements on an individual bike can provide a general answer to this question since it certainly will depend on the details of the engine (valve overlap, presence or absence of a balance pipe on a twin, etc.) and exhaust system (open pipe, megaphone, restrictive silencer, etc.).

In summary, if the exhaust sensor is installed in a bung welded in a "good" place in the exhaust pipe it will accurately determine the AFR. If in a "bad" place it either will measure a value so far off that there won't be any chance of thinking it is real, or risk damage or error caused by too-hot gas. If the sensor is in a separate probe inserted past the point of reversion it will accurately determine the AFR, but that AFR could be somewhat different than it would be without the probe affecting the pressure pulses.
1 member likes this
by kevin
not only reversion at the back end, but percentage of complete combustion at the front end.

the O2 sensor measures oxygen in the exhaust gas as it passes the sensor. it doesn't measure oxygen in the combustion chamber before the exhaust valve opens. the combustion chamber mixture is what we'd like to measure, but burning is never instantaneous.

if there is mixture still burning in the exhaust gases as they travel down the pipe, then the amount of free oxygen in the exhaust gas will not reflect what the combustion chamber saw during the power and exhaust stroke.

how much does mixture continue to burn in the exhaust? if the exhaust opens early, if the ignition timing is late, if the mixture is super lean, then burning may still be going on in the mixture as it passes the exhaust valve and heads down the pipe. whatever concentration of oxygen the pipe sees is incompletely correlated with what the combustion chamber saw before.

lots of variables that are hard to control. think about what a leaky exhaust flange could do to your readings
1 member likes this
by Magnetoman
Originally Posted by kevin
lots of variables that are hard to control.
You may be overthinking the hypotheticals. Although various things could go wrong in the AFR determination, in my experience it's not too hard in a typical setup to be sure none of them do. However, that still leaves a big uncertainty to deal with; what AFR to aim for.

These days any random refueling stop could leave your tank filled with fuel containing anywhere from 0% to 15% ethanol, i.e. fuels having stoichiometric ratios from 14.7 to 13.8. It's important to note that even if a pump is marked, say, "E10" or "E15", U.S. regulations allow the ethanol content to be up to 10% and 10.5–15%, respectively, so the "E10" you use when jetting your carburetor could very well be different than the "E10" you fill your tank with on a subsequent refueling stop.

Maximum power for "pure" gasoline is obtained at an AFR of 12.5–13.2, while for an E15 blend containing an actual 15% ethanol that needs to be 11.7–12.4, instead. Unfortunately, if your AFR display unit uses a fixed value of 14.7 to calculate the number it displays, the "AFR" on the display would be wrong by the ratio 13.8/14.7 with that E15, i.e. by 6.5%.

Luckily, there's an easy way around this issue since, independent of the fuel, maximum power is obtained at the same λ ≈ 0.85–0.90. All gauges that use these wide-band sensors intrinsically measure λ and then at least some of them calculate the AFR assuming the 14.7 of "pure" gasoline (unless they're programmable with different values for stoichiometry). So, forget about AFR, set your unit to display λ, and jet your carburetor to result in λ ≈ 0.85–0.90 for the fuel you will be using, whether it be "pure" gasoline or E15, or anything in between.

Unfortunately, the above doesn't solve the deeper problem, that the actual ethanol content of the fuel you buy at any given time is a crapshoot. However, for anyone not needing the absolute max. hp their engine is capable of producing, this turns out not to be a problem.

What AFR of 13.8 vs. 14.7 means is E15 requires less air than gasoline does for a fixed amount of fuel. Or, equivalently, more fuel for a fixed amount of air. Since your engine sucks in a fixed amount of air on each stroke, and if you jet your carburetor perfectly with gasoline, it will run leaner with E15. But, only 6.5% leaner. If you do your jetting with a gallon of expensive ethanol-free gasoline purchased from a speed shop, and jet it at the 0.85 rich end of the λ range, if you subsequently fill your tank with E15 having the full 15% ethanol composition, λ would be 14.7/13.8 × 0.85 = 0.905. That means you'll still be fine. If the ethanol content is less than 15% it only improves a situation that doesn't even need improving. Actually, even if you use gasoline to jet it at 0.9, with E15 that will be 0.96. You'll lose a bit of h.p. but even 1.06 shouldn't be a problem for the engine.

For now, at least, the variable and unknown ethanol content easily can be reduced to a non-issue, leaving octane as the final parameter to worry about (at least, for those of us with 10:1 pistons in our Gold Stars).
1 member likes this
by kevin
magneto is right about fuel blending making a difference with AF ratios.

look over this
1 member likes this
by gunner
For info Gavin my B44 runs a JRC PWK 28mm with the following jetting though this may well be different on your bike:-
- main jet 130
- pilot jet 30
- needle clip position middle
- needle type JJM (straight section diameter 2.475)
- air screw 1 1/2 turns out

When I originally installed the carb I found it was running rich. I eventually found that the needle was too narrow and fitted a JJM needle which has a thicker straight section and allows less fuel to bleed past the jet.

As received the JRC PWK didnt have any markings on the jets, so I swapped the jets for genuine Keihin PWK 28 jets which are readily available.

I note that the PWK seems to come in 3 size ranges with different jets for each, 24-26mm, 28mm and 32-34mm. I would buy a set of needles and other jets for your OKO 32mm from some where like This Site which has a good selection.

Previously I was using Allens Performance for PWK jets but they dont seem to list 32mm as a size but they do have useful info on the needle dimensions for other PWK carbs see THis Link
1 member likes this
by GrandPaul
Should be...
1 member likes this
by gavin eisler
gavin eisler
Well its been a long winter, the Air Fuel Ratio thing is 1/2 a step closer, I got a bung, m18 x 1.25, lambda port bung, to plug the port once its welded on, the cabling is extensive and may need to be cut down, the bracket for the dial is good , doesnt flutter, but blocks all the idiot lights, I quite like the serenity.
I hope to bang out the exhaust dent from the prang a cuppla years ago through the hole cut for the lambda probe, this will put it on the primary side , about level with the pipe bracket pointing back horizontal.
Put a cuppla tankfuls through , speedo isnt right, fluttering and lagging past 50 mph, the rear drive is shagged, new one from ebay 44quid delivered.
The old one has failed where the nut seized then the neck broke trying to undo it, entropy, and too much force.Salt.

Other than that , I changed the kick start lever to a folding type, and copied the gear pedal in Alloy, it was tricky to get the kick swing to clear the pedal, but this version seems to work . I have stopped carrying the old pedal with me . The old pedal and me go back a long way, it was on it when I got it,it has always wobbled after 50 miles , and fallen off at least twice not many parts as peripheral can say that..The yellow nickel of the new kick lever is weird, chrome is much bluer.

Changed the fluids, V clean, g box and primary still a hint of red, pretty black motor oil, least fur yet on the sump magnet
Spent an afternoon tracing a poor dip beam , low volts, found two bad connections, one super sloppy crimp, I was shocked, another bullet that needed snapping back in, possibly pulled in the prang that took out the forks.

The centre stand has got to go, when the side stand fails I will put it back on.

The new kick lever is in a different place , longer , mebbe meant for a B50.10:1 would be easy.
When riding the lever is more out of the way and gets my shin in more, the new gear pedal feels good and looks less scabby.
I did a trial fit with the new set of pipes, took the old set off to clean up the TS which was chuffing at the head port, wonder of wonder, the new set has a decent balance pipe line up with the pipes in the head, YAY, , boo to the missaligned DS motor/ frame tab which is short by about an eight and aff the batter by a quarter down and 1/2 " back. These will work tho, will do like Triumph , cut the noo pipes brackets to a tab, then join them to L brackets with a bolt.
Will fill in pics soon, the timing side looks different.

Other than that, I didnt clean the carbs or dump the fuel over winter, it just started up, not even charged the battery, I might change the spark plugs just because they are now V rusty. Bike continues to run V well, now loose and revvy, the gear box initial stiffness is gone , the ratios make riding a lot easier, as it loosens up it becomes more and more like riding a two stroke, keeping it on the cam is loads of fun. Vibration through the footrests seems to be linked to rear drive chain wear, smooth until the chain is tired,.
Next tyre change goin for TT a hunders, Ali has a cheap one in the shop, 4.25, maybe too wide, he needs the space.
I have a spare head and flow chamber/ bench in the pipeline, got stung by a FB guy, on valve gear stuff, he has one more chance to come good, then names will be named, . once i get the Air Fuel stuff working on the xisting set up , I will half half an idea of how to set up the OKO carbs.
1 member likes this
by Bougor
The body of the sensor may be ground; worth checking.

1 member likes this
by gavin eisler
gavin eisler
The wrapper on the down pipes says LF Harris. I got them from Grins , with fair warning that they may need tweaking, I think it was his last set, not listed on his site anymore.
1 member likes this
by gavin eisler
gavin eisler
Not much input for a while, no news is good news eh.
Auto jumble scores, a NOS set of balnced exhaust pipes and a good breadbin tank from a T that has the fuel taps in a better forward location and no dents yay.

A week or two ago on the return from the chipper the bike started running on one pot, hmmm, low fuel |I thought , put on reserve and got home OK ish.

Next start with an added gallon of fuel, starts ok, set off for the petrol pumps, at the end of the road starts missing, cuts out totally about a 1/4 mile later. Long hot push home, bugger.

Investigating further, found serious water contamination of the fuel, not straight away, first suspect was carb rubbers has split, fitted new set , no change. All carb faults are electrics aren, they?, looked at the wiring , noted TS coil LT terminals had melted the wee blobs of solder on the top of the studs, hmm, checked wiring , found a dry / corroded crimp replaced that on the black yellow core , no difference, thats when I found the water in the fuel.

Fixed the rocker cover leak, the cover was distorted with a gap at the front DS lobe, sanded it flat , reset the tappets, ( exh had closed a tad).

Ordered up a new pair of carb to airbox rubbers, old set has chafed through, .Ordered spare rocker cover gaskets.
1 member likes this
by Hugh Jörgen
Hugh Jörgen
1 member likes this
by Dibnah
That was a good read, thanks Gavin. I am envious of your local backroads, although the midges and the tourists would be annoying.
1 member likes this
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